There are currently no cures for over thirty types of inherited muscular dystrophies that affect people worldwide. The common feature in these diseases is progressive muscle weakness and loss of muscle strength. However, progression of the disease varies considerably in the muscles affected, severity, and age of onset. While many studies have been done to examine the triggers and resulting physiological changes associated with muscle wasting, details concerning the molecular basis of these diseases are only emerging. A better understanding of the molecular players involved in muscular dystrophies and atrophic muscle must first be established before truly successful therapeutic strategies can be developed. Our long term goal is to understand the molecular events responsible for muscle protein turnover and how misregulation of this process results in muscular dystrophies and atrophy. The overall objective of this application is to use the genetically tractable organism Drosophila melanogaster to develop an in vivo model for muscle wasting diseases, specifically Limb-Girdle Muscular Dystrophy type2H (LGMD2H). Our rationale for this project is that LGMD2H is caused by a mutation in the muscle-expressed E3-ubiquitin ligase protein TRIM32. Using the fruit fly, we have found a similar gene, dTRIM32, which is expressed in both embryonic and mature muscle tissues. The genetic and molecular tools available in the fly make it an ideal organism to model human disease, as the fly offers shorter generation times and less functional redundancy than found in vertebrate genomes. We have extensive experience using Drosophila genetics to uncover gene function and we have developed an in vivo biochemistry/mass spectrometry approach for identifying potential substrates of dTRIM32. We therefore plan to achieve our objective by pursuit of the following three specific aims: 1) to phenotypically characterize dTRIM32 deficient flies in myoblast fusion and adult muscle structure;2) to determine which regions of dTRIM32 are important for muscle function and/or myofibril structure;and 3) to identify and characterize new target substrates for the Drosophila E3-ubiquitin ligase dTRIM32 in the developing embryonic muscle and adult muscle by mass spectrometry. PUBLIC HEALTH RELEVANCE: While many studies have been done to examine the triggers and resulting physiological changes associated with muscular dystrophies, details concerning the molecular basis of these diseases are only emerging. The studies proposed herein are designed to gain a better understanding of muscle protein turnover and how misregulation of this process may result in muscle atrophy. A better understanding of the molecular players involved in muscular dystrophies and atrophic muscle must first be established before truly successful therapeutic strategies can be developed.